Thermal diffusion apparatus



Feb. 25, 1958 D. FRAZIER THERMAL DIFFUSION APPARATUS Filed June 20, 1956 SCHEMATIC ILLUSTRATION OF THERMAL DIFFUSION APPARATUS F/Gl INVENTOR. DAVID FRAZIER A ORNEY his United States Patent 2,824,647 THERMAL DIFFUSION APPARATUS David Frazier, Cleveland Heights, Ohio, assignor to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio Application June 20, 1956, Serial No. 592,664 3 Claims. (Cl. 210-176) This invention relates to apparatus for separating a fluid mixture into separate fractions by thermal diffusion, one of the fractions being enriched with at least one of the initial components in the fluid mixture and another fraction being enriched with a different component initially in the fluid mixture.

It has been known for some time that a fluid mixture, i. e., a mixture of liquids or a mixture of gases, can readily be separated into dissimilar fractions upon being confined in a narrow chamber across which a temperature gradient is imposed by relatively heating and cooling opposed chamber-forming wall surfaces. When such a chamber is substantially vertical, one of the dissimilar fractions having a higher than initial concentration of one component preferentially accumulates adjacent the relatively heated or hot wall and another fraction having a higher than initial concentration of a different component preferentially accumulates adjacent the relatively cooled or cold wall. Differences in density cause the fraction adjacent the hot wall to ascend within the chamber and the fraction adjacent the cold wall to descend or, in effect, induce a thermal circulation or convection.

While there is evidence to show that rather remarkable separations are thus actually effected within a thermal diffusion chamber, considerable difliculties have been encountered in attempts to take advantage of the separation thus obtained. This is mainly due to the fact that the spacing between opposed walls of a thermal diffusion separation chamber is at most only a fraction of an inch, i. e., of the order of less than one-half inch, and preferably less than 0.15 inch, e. g., about 0.02 to 0.06 inch, for liquid separation and about 0.2 to 0.3 inch for separation of gases and to the inherent physical difliculty of dividing such a narrow stream of fluid into two separate portions.

In accordance with the present invention, the separate removal of dissimilar fluid fractions separated in a thermal diffusion separation chamber is accomplished with greater efficiency than by any means believed heretofore to have been proposed, by so constructing the apparatus that the fraction preferentially advancing toward a given end of a thermal diffusion separation chamber is induced to flow beyond the end of the chamber without any substantial change in speed or direction for a distance sufiicient to avoid appreciable mixing or re-mixing with fresh fluid or other components and fractions. This is accomplished with an annular thermal diffusion separation chamber or column formed by inner and outer concentric, substantially vertical tubes by increasing the diameter of the outer tube at one end while maintaining the diameter of the inner tube constant so as to define a first annular reservoir communicating with one end of the separation chamber and at the other end reducing the diameter of the inner tube while maintaining the diameter of the outer tube constant so as to'define a second annular reservoir communicating with the other end of the annular thermal diflusion separation chamber. Means are provided for relatively heating the tube having a change in diameter ascending fraction adjacent the hot wall into the upper a I reservoir and an uninterrupted movement of the descend- 'ice ing fraction adjacent the cold wall into the lower reservoir. Means are also provided for introducing fluid mixture into the upper and lower reservoirs in such manner as to minimize mixing with the ascending and descending fractions, respectively, and for separately withdrawing said fractions from the reservoirs.

In the preferred embodiment of the invention, an annular thermal diffusion separation chamber is formed by a set of concentric tubes in which the lower end of the inner tube is of reduced diameter and the upper end of the outer tube is of increased diameter. The outer surface of the inner tube and the inner surface of the outer tube form an annular separation chamber between an upper reservoir formed by the upper end of the inner tube and the upper end of increased diameter of the outer tube and the lower reservoir formed by the lower end of the inner tube of decreased diameter and the outer tube. The spacing between the outer surface of the inner tube and the inner surface of the outer tube is preferably less than 0.15 inch and more generally of the order of 0.02 to 0.06 inch in the annular thermal diffusion separation chamber when'separation of liquids is desired and somewhat greater, i. e., up to about one-half inch, and preferably between about 0.2 and 0.3 inch, when separation of gases is desired. The upper and lower reservoirs should be of sufficient volume to avoid a turnabout of the fluid within the separation chamber before it reaches the reservoir. Generally, this effect is obtained when the spacing between the opposed surfaces of the inner and outer tubes at the upper and lower reservoirs is considerably greater, preferably at least about two times that of the spacing within the thermal diffusion separation cham her and the depth of the reservoirs is likewise at least about twice the spacing of the opposed chamber-forming wall surfaces. In the preferred structure described, means are provided for relatively heating the inner tube and relatively cooling the outer tube.

It is to be understood that the preferred structure may also be reversed to the extent that if the upper reservoir is formed by decreasing the diameter of the inner tube while maintaining the diameter of the outer tube constant and the lower reservoir is formed by increasing the diameter of the outer tube while keeping the diameter of the inner tube constant, means. are provided for relatively cooling the inner tube and relatively heating the outer tube.

It has also been found advantageous to utilize a number of the thermal diffusion columns of this invention in series wherein the dissimilar fractions withdrawn separately from the upper and lower reservoirs of one column are discharged into the upper and lower reservoirs of adjacent columns in the series. This is particularly advantageous when the interconnection between the upper and lower reservoirs for the series of thermal diffusion separation chambers is such that the fresh fluid is fed to the upper reservoir for the first in the series of chambers and to the lower reservoir in the last of the series of chambers, the fraction withdrawn from the upper reservoir for the first chamber in the series is transferred to the upper reservoir for the second chamber in the series and so on until it is finally withdrawn from the upper reservoir for the last in the series of chambers, and the fraction with-drawnfrom the lower reservoir for the last in the series of chambers is transferred to the lower reservoir for the next to the last in the series of chambers and so on through preceding lower reservoirs until it is finally withdrawn from the lower reservoir for the first in the series of chambers.

When the fluid to be subjected to separation by thermal diffusion is a liquid and a number of separation chambers are interconnected in series, it is most desirable to provide meafisfsu'ch' asstandpipes or the like, as

compensate for differences in the average densities of the liquids in the various columns and thereby avoid convective inter-chamber circulation due to differences in density that could, under some circumstances, promote undesirable re-mixing of separated components.

The apparatus of the invention will become further apparent from the following detailed description made with reference to the accompanying drawing illustrating the best mode contemplated of carrying out the invention.

In the drawing, Figure 1 is a schematic illustration, in elevation, showing a number of thermal diffusion separation columns constructed in accordance with the invention that are connected in series.

Three annular thermal diffusion separation chambers 10, and 30 are shown as formed between the outer surfaces of inner tubes 11, 21 and 31 and the inner surfaces of outer tubes 12, 22 and 32. Upper reservoirs 13, 23 and 33 are formed between the outer surfaces of the inner tubes and the inner surfaces 14, 24 and 34 of the upper portions of increased diameter of the outer tubes. Lower reservoirs 15, 25 and 35 are formed between the inner surfaces of the outer tubes 12, 22 and 32 and the outer surfaces 16, 26 and 36 of the lower portions of reduced diameter of the inner tubes. Feed ports 17, 27 and 37 are preferably provided for the upper reservoirs 13, 23 and 33 adjacent the upper ends of the annular chambers 10, 20 and and feed ports 18, 28 and 33, preferably extending into the lower reservoirs 15, 25 and a distance at least half the spacing between the opposed wall surfaces of the inner and outer tubes are provided for said lower reservoirs. Withdrawal ports 19h, 29/1 and 3911 are provided at the tops of the upper reservoirs 13, 23 and 33, withdrawal ports 19]: and 2911 being connected to feed ports 27 and 37, respectively, and withdrawal ports 19c, 22c and 390 are provided at the lower ends of the lower reservoirs 15, 25 and 35, withdrawal ports 29c and 39c being connected to feed ports 18 and 28, respectively. The upper reservoirs are, when columns are connected in series, provided with suitable standpipes for equalizing the average densities in the different columns and thus avoiding inter-column circulation based on any such density differences. Thus, for example, when the average density in the last of a series of columns is the lowest, inter-column circulation that may be harmful as avoided by the standpipes or other means such as raising the elevation of the last column with respect to the preceding column. With standpipes under such conditions, the level in the standpipe for the last column would be higher (as illustrated in the drawing) than that in the standpipe for the previous column I so that the total weight of liquid in the last two columns will be equal. Any suitable means, such as for example steam and circulating cold water, may be provided for relatively heating the inner tubes 11, 21 and 31 and relatively cooling the outer tubes 12, 22 and 32.

In operation, the outer tubes 12, 22 and 32 are relatively cooled, e. g., by immersion in circulating tap water, and the inner tubes 11, 21 and 31 are relatively heated, e. g., by passing through them steam under pressure, to impose a temperature gradient across the annular separation chambers 10, 2t and 30. Fresh fluid mixture is continuously introduced by way of entry ports 17 and 33. When the columns and reservoirs are filled, feed of the fluid mixture is continued while fractions preferentially accumulating adjacent the hot and cold walls ascend or descend, as the case may be, to enter the upper and lower reservoirs by movement along the tube surfaces of unchanged diameter, i. e., the upper portions of the inner tubes and the lower portions of the outer tubes. The feed entering the reservoirs through ports 17, 27, 37, 18, 28 and 38 enters the annular chambers 10, 20 and 39 to replace the ascending and descending fractions which are either transferred to the corresponding reservoir of the next adjacent column or withdrawn as separate products through withdrawal ports 39h and 190.

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It is to be expected that various modifications will readily become apparent to those skilled in the art upon reading this description. All such modifications are intended to be included within the scope of the invention as defined in the appended claims.

I claim:

1. Thermal diffusion apparatus for separating a fluid mixture into fractions enriched with dissimilar components which comprises concentric, substantially vertical tubes defining between the outer surface of the inner tube and the inner surface of the outer tube an annular thermal diffusion separation chamber, one end of the outer tube having an increased diameter and de fining, with the outer surface of the inner tube, a first annular reservoir communicating with one adjacent end of the thermal diffusion separation chamber and the other end of the inner tube having a reduced diameter for defining, with the inner surface of the outer tube, a second annular reservoir communicating with the other adjacent end of the annular thermal diffusion separation chamber; means for relatively heating the tube having a change in diameter at the lower end and relatively cooling the other tube to maintain a temperature gradient across the annular thermal diffusion separation chamber and separate liquid mixture in the chamber into an ascending fraction enriched in one dissimilar component and a descending fraction enriched in another dissimilar component; means for continuously introducing fluid mixture into the upper and lower reservoirs; and means for separately and continuously withdrawing from the upper and lower reservoirs fractions enriched with the dissimilar components contained in higher than initial concentrations in the ascending and descending fractions.

2. Thermal diffusion apparatus for separating a fluid mixture into fractions enriched with dissimilar components which comprises concentric, substantially vertical tubes defining between the outer surface of the inner tube and the inner surface of the outer tube an annular thermal diffusion separation chamber, the upper portion of the outer tube having an increased diameter and defining, with the outer surface of the inner tube, an upper annular reservoir communicating with the upper end of the thermal diffusion separation chamber and the lower portion of the inner tube having a reduced diameter for defining, with the inner surface of the outer tube, a lower annular reservoir communicating with the lower end of the annular thermal diffusion separation chamber; means for relatively heating the inner tube and relatively cooling the outer tube to maintain a temperature gradient across the annular thermal diffusion separation chamber and separate liquid mixture in the chamber into an ascending fraction enriched in one dissimilar component and a descending fraction enriched in another dissimilar component; means for continuously introducing fluid mixture into the upper and lower reservoirs; and means for separately and continuously withdrawing from the upper and lower reservoirs fractions enriched with the dissimilar components contained in higher than initial concentrations in the ascending and descending fractions.

3. Thermal diffusion apparatus for separating a fluid mixture into fractions enriched with dissimilar components which comprises a series of annular thermal diffusion separation chambers provided with upper and lower reservoirs as defined in claim 1, wherein the means for introducing fluid mixture into the upper reservoirs for the intermediate and last chambers in the series are connected to the withdrawal means for the upper reservoirs for the next preceding chambers; and the means for introducing fiuid mixture into the lower reservoirs for the intermediate and first chambers in the series are connected to the withdrawal means for the lower reservoirs for the next succeeding chambers in the series.

No references cited. 

1. THERMAL DIFFUSION APPARATUS FOR SEPARATING A FLUID MIXTURE INTO FRACTIONS ENRICHED WITH DISSIMILAR COMPONENTS WHICH COMPRISES CONCENTRIC, SUBSTANTIALLY VERTICAL TUBES DEFINING BETWEEN THE OUTER SURFACE OF THE INNER TUBE AND THE INNER SURFACE OF THE OUTER TUBE AN ANNULAR THERMAL DIFFUSION SEPARATION CHAMBER, ONE END OF THE OUTER TUBE HAVING AN INCREASED DIAMETER AND DEFINING, WITH THE OUTER SURFACE OF THE INNER TUBE, A FIRST ANNULAR RESERVOIR COMMUNICATING WITH ONE ADJACENT END OF THE THERMAL DIFFUSION SEPARATION CHAMBER AND THE OTHER END OF THE INNER TUBE HAVING A REDUCED DIAMETER FOR DEFINING, WITH THE INNER SURFACE OF THE OUTER TUBE, A SECOND ANNULAR RESERVOIR COMMUNICATING WITH THE OTHER ADJACENT END OF THE ANNULAR THERMAL DIFFUSION SEPARATION CHAMBER; MEANS FOR RELATIVELY HEATING THE TUBE HAVING A CHANGE IN DIAMETER AT THE LOWER END AND RELATIVELY COOLING THE OTHER TUBE TO MAINTAIN A TEMPERATURE GRADIENT ACROSS THE ANNULAR THERMAL DIFFUSION SEPARATION CHAMBER AND SEPARATE LIQUID MIXTURE IN THE CHAMBER INTO AN ASCENDING FRACTION ENRICHED IN ONE DISSIMILAR COMPONENT AND A DESCENDING FRACTION ENRICHED IN ANOTHER DISSIMILAR COMPONENT; MEANS FOR CONTINUOUSLY INTRODUCING FLUID MIXTURE INTO THE UPPER AND LOWER RESERVOIRS; AND MEANS FOR SEPARATELY AND CONTINUOUSLY WITHDRAWING FROM THE UPPER AND LOWER RESERVOIRS FRACTIONS ENRICHED WITH THE DISSIMILAR COMPONENTS CONTAINED IN HIGHER THAN INITIAL CONCENTRATIONS IN THE ASCENDING AND DESCENDING FRACTIONS. 